Throughout the industrialized world there are deposits of contaminated soil which pose a hazard. Ground water which enters these contaminated soils can dissolve and carry some of the contaminants into drinking water supplies. The contaminants include such materials as harmful organic compounds and soluble heavy metals. In some cases the soils are contaminated with radioactive wastes.
In some serious cases, contaminated soils are removed and treated in furnaces to produce vitrified masses of material. When contaminated soil is vitrified, its density is increased and its volume is reduced. Additionally, organic compounds are typically pyrolized and rendered harmless. When a mass of contaminated soil is vitrified, it can be safely buried in the earth because any heavy metal components of the soil are made substantially unleachable in ground water.
In addition to contaminated soils, there are other hazardous objects which require safe disposal. For, example obsolete military devices such as fuses and chemical warfare apparatus need to be destroyed in a cost-effective way. In many of these cases, for purposes of maintaining secrecy, there is a need to obliterate any discernible features or characteristics of the devices. Disposal of such devices in a vitrified soil medium has been found to be technically and economically viable.
Centrifugal plasma arc furnaces have been employed with some limited success to perform these disposal tasks. One such furnace is described in U.S. Pat. No. 5,136,137 (M. P. Schlienger), issued Aug. 4, 1992. In principle, this furnace is operated in a semi-batch mode. Materials to be treated are fed into a refractory lined rotatable chamber. A plasma arc torch heats the material in the chamber as it rotates. The material melts and forms a slag. Material is continually fed into the chamber until a predetermined mass of material is in a molten form. The chamber is then stopped and the slag is poured out of the chamber into a container. After the chamber is emptied, the process of introducing material and melting with the plasma arc torch is repeated.
The principle of operation of a centrifugal plasma arc furnace is well-described in the above identified U.S. Patent and various other patents which have issued from related applications. These patents however do not describe a practical method for operating the centrifugal plasma arc furnace to achieve a cost-effective waste disposal system.
We have found that the furnace suffers from various shortcomings which have heretofore precluded its economic application to real-life disposal problems. For example, we have observed that the furnace can not be operated successfully be simply introducing waste materials of any variety into the rotating chamber. In many cases, the waste materials form a molten slag which is too highly viscous. Highly viscous molten slags typically will not pour out of the chamber. This problem is particularly acute when stainless steel objects are part of the waste materials. When the chamber cannot be easily emptied, the furnace cannot operate as a high productivity commercial unit but is instead relegated to operation as a laboratory experimental device.
It is desirable therefore to provide a method that will facilitate the use of a centrifugal plasma arc furnace to process large quantities of contaminated materials in a cost-effective and efficient manner.